Make-alive electrode for vaporelectric converters



Aug. 19, i941.- L HAN ETAL 2,253,402

MAKE-ALIVE ELECTRODE FOR VAPORELECTRIC CONVERTERS Filed June 15, 1939WITNESSES: INYENTORS I Q Joseph Sleptan and Herbert A.H0se.

AIZTORNEY Patented Aug. 19, 1941 UNITED STATES PATENT OFFICE MAKE-ALIVEELECTRODE FOR VAPOR- .ELECTRIC CONVERTERS Joseph Slepian,Pittsburgh, Pa,and Herbert A.

Rose, Belle Meade, N. .I., assignors to Westinghouse Electric &Manufacturing Company, East Pittsburgh, Pa., a corporation ofPennsylvania Application June 13, 1939, Serial No. 278,842

I separated therefrom, and a make-alive electrode 4 Claims.

than heretofore. More specifically stated, it is an object of ourinvention to surround the makealive rod with a longitudinally slottedinsulating sheath which causes the mercury to reach the make-alive rodthrough a convex meniscus, so that the surface-tension of the mercury,at the surface of the meniscus, is pulling away from the make-alive rod,in opposition to the head of mercury dependent upon the depth of themeniscus at any point, as distinguished from previous constructions inwhich the mercurysurface which was in contact with the sides of themake-alive rod had a concave or circular configuration, embracing therod, so that the surface-tension of the mercury tends to pressthemercury against the make-alive rod, adding its pressure to themercury-head dependent upon the depth of the various points in thecontact. The result of the decreased contact which is achieved by ourinvention is an increasein the efliciency of the make-alive electrodeand a reduction in the necessary current in the makealive circuit.

With the foregoing and other objects in View, our invention consists inthe elements, parts,

combinations, apparatus and methods hereinafter described and claimed,and illustrated in the accompanying drawing; wherein Figure 1 is adiagrammatic view of circuits and apparatus illustrating the generaltype of combination in which our invention is adapted to be utilized,

Fig. 2 is an enlarged detailed vertical-elevational view showing ourimproved makealive electrode in the mercury cathode, the sectionplanebeing indicated by the line 11-11 in Fig. 3, and i Fig. 3 is ahorizontal sectional View thereof, on the line III-III of Fig. 2.

Our invention applicable to the general type of converter. which isillustrated, in Figure 1, as comprising a; vaporizable liquid cathode 4,which may be mercury, an anode 5 spaced or 6 which projects into thecathode 4, all enclosed within a container which is diagrammaticallyrepresented at 1. The make-alive 6 may be energized in any one of anumber of difierent ways,

' Fig. 1 showing a conventional form of circuitin which the make-aliveis connected to the anodelead 8 through a small auxiliary rectifier 9.

The particular form of make-alive electrode 6, which is utilized in ourinvention, is illustrated, on an enlarged scale, in Figs. 2 and 3. Itcomprises a rod-like core H of a high-resistance make-alive materialwhich may be practically any high resistance material which does notamalgamate with mercury, or in general, with the cathode-material 4,suchas boron carbide, or well known make-alive equivalents. This make-alivecore or rod H is enclosed in a fairly closely fitting, or adhering,sheath [2 of any suitable insulating material which may be quartz,ceramic material, or vitreous material. It is obvious that the materialof the insulating sheath l2 should be capable of withstanding thethermal expansions and contractions of the make-alive core II, as wellas the maximum operating temperature which is encountered. The sheath I2is provided with one or more longitudinal slots l3, one being shown,which extends substantially vertically when the make-alive electrode 6is immersed into the mercury, in its normal operating position.

tion, as shown in Fig. 3.

The efiect of the slotted insulating sheath I2 is to cause the mercury 4to reach the make-alive core ll, through the vertical slot l3, by meansof a meniscus I4 which is convex in cross-sec- This meniscus has aradius of curvature which, at its greatest, is of the order of one-halfof the width 111 of the slot i3, as shown in Fig. 3. The thickness ofthe insuiating wall of the sheath [2 is preferably of the same order ofmagnitude as this maximum radius of curvature of the meniscus I4, asalso illustrated in Fig. 3, so that the meniscus is capable of justbarely lightly touching the makealive rod II, with a zerocontact-pressure, at the top point l5 (Fig. 2) where it first makescontact.

At this top contact-point I5, the surface-tension T of the mercury (orother cathode-material) pulls the meniscus I 4 in a direction away fromthe make-alive rod II with two forces l6, equal to the surface-tensionT, as indicated in Fig. 3, and this total force is exactly opposed bythe pressure-head due to the weight of a mercury-column corresponding tothe depth d of the point I will be 2T=Gwd (1) In the case of mercury,the surface-tension T is .0475 gram per millimeter and the specificgravity G is .0136 gram per square millimeter, so that the formulabecomes wd=7, (in millimeters) In accordance with our invention, it isdesired to have the top contact-point I5 at a depth d of a fewmillimeters, or anywhere from about 4 millimeters to, say, 20millimeters, although these limits are by no means critical. Theselimits correspond to a slot-width w of 1.75 millimeters and .35millimeter, respectively. The thickness of the insulating sheath I2should be at least something commensurate with the radius of themeniscus M, which is 20/2, giving a minimum sheath-thickness of, say,about 0.1 millimeter. We have found that a slot-width w of 0.6millimeter is satisfactory, and we should say that the slot-width wshould be not more than about 2 millimeters and not less than about 0.2millimeter, for a mercury cathode.

The functional effect of our invention will best be understood bycomparing it with the operation which is obtained with a barecylindrical member sticking into the mercury, as in the case of previousmake-alive electrodes. In Fig. 2, a slot I3 is shown on the right-handside of the makealive electrode, and a plain cylindrical wall I2 on theleft-hand side.

For the purpose of our present discussion of the contact-pressurebetween the mercury and the make-alive electrode, we may consider thatthe plain cylindrical wall I2 on the left-hand side of the figurecorresponds to the outer periphery of a plain, prior-art make-aliveelectrode without the slotted insulating sheath of our presentinvention. It will be observed that the mercury meniscus I'I brings thetop contact-point I8 down to a depth do below the top surface of themercury. This depth do may be roughly of the order of two millimeters,making the static pressure-head something like .027 gram per squaremillimeter. At and below this point I8, however, if the outer surface ofthe make-alive were a plain cylinder having a radius R, the surface ofthe mercury in contact with it would also be the same cylinder having aradius R millimeters, so that the surface-tension T of the mercury (ingrams per millimeter) would tend to constrict this cylindrical surface,with a pressure of T/R grams per square millimeter. If the radius R ofthe makealive was, say, two millimeters, the constrictive force of thesurface tension of the cylindrical mercury-surface surrounding themake-alive electrode would be .024 gram per square millimeter, or ofabout the same order of magnitude as the static pressure-head of .027gram .per square millimeter at this top contact-point I8, correspondingto the operation obtained with a plain uncovered make-alive electrode.These two pressures would be additive, giving a total contact-pressureof about .051 gram per square millimeter at the top contact-point I8.From this point down, the contact-pressure between the mercury and thecylindrical outer surface of the make-alive electrode will steadilyincrease in proportion to the total depth d at any point.

In contrast with this operation of previous make-alive electrodes, themercury does not get down (or over) to the bottom of our slot I3 until apoint I5 is reached, which is below the point I8 at the bottom of theannular meniscus I7, and at this initial, or top, contact-point I5, themercurypressure, instead of having a finite positive value of .05 ormore grams per square millimeter, will actually have a zerocontact-pressure. Under these conditions the convexly curved surface ofthe mercury meniscus I4 will just barely lightly touch the highest spotsof the rough cylindrical surface of the make-alive rod II. Below thispoint I5, the contact-pressure of the mercury increases in accordancewith the depth of the mercury, being always equal to the total staticpressure-head at any depth d, minus the initial static pressure-head ofthe point I5. In addition to this reduction in the contactpressure ofthe mercury against the surface of the make-alive rod II, our structurealso results in a very considerable reduction in the area of thecontacting surface between the mercury and the make-alive rod I I. Thiscontact area starts with a straight line at, and immediately below, thetop contact-point I5 (neglecting, for the moment, the inevitableirregularities in the surface of the make-alive rod), and as the depthincreases, the static pressure-head gradually flattens out the meniscusI4 so that it makes contact with the make-alive rod II over a larger andlarger proportion of the total width w of the slot I3. It is plain tosee that the total overall contact-pressure of the mercury that comesinto contact with a side of the make-alive rod II through the verticalslot I3 is very much less than the area of the whole cylindrical surfacebelow the point I8, which would be the contactsurface if our slottedshield I2 were not utilized. This reduction in the contact-area, coupledwith our reduction in the contact-pressure, results in a make-aliveelectrode which operates more effectively, and consumes much lesscurrent, or electrical energy, than in previous make-alives.

While we have described our invention in a preferred form ofconstruction utilizing a single slot I3' of uniform width w, formed inan insulating sheath I2 having walls of uniform thickness, andsurrounding a make-alive rod II of uniform cross-sectional area, it willbe obvious that our invention is not limited to these details, and thatthese and other features may be changed by those skilled in the artwithout departing from the basic principles of our invention. We desire,therefore, that the appended claims shall be given the broadestconstruction consistent with their language and the prior art.

We claim as our invention:

1. A make-alive electrode for a vapor-electric converter of a typehaving a vaporizable liquid cathode, an anode separated from saidcathode, and a make-alive electrode projecting into said cathode, saidmake-alive electrode comprising a rod-like core of a high-resistancemake-alive material and a closely fitting slotted sheath of insulatingmaterial, said sheath having a thickness of at least about 0.1millimeter and havinga longitudinally extending slot extending throughthe wall thereof, said slot having a width of at least about 0.2millimeter and not more than about 2 millimeters, the width of the slotbeing so dimensioned, within said limits, as to cause the meniscus ofthe cathode to barely touch said core with a substantially zero pressureat some point below the level of the cathode.

2. A make-alive electrode for a mercury-arc converter of a type having amercury cathode, an anode separated from said cathode, and a make-aliveelectrode projecting into said cathode, said make-alive electrodecomprising an approximately smooth-surfaced rod-like core of ahigh-resistance make-alive material and a closely fitting slotted sheathof insulating material, said sheath having a thickness of at least about0.1 millimeter and having a longitudinally extending slot extendingthrough the wall thereof, said slot having a width of at least about 0.2millimeter and not more than about 2 millimeters, the width of the slotbeing so dimensioned, Within said limits, as to cause the meniscus ofthe cathode to barely touch said core with a substantially zero pressureat some point below the level of the cathode.

3. A vapor-electric converter comprising a vaporizable liquid cathode,an anode separated from said cathode, and a make-alive electrodeprojecting into said cathode, characterized by said make-alive electrodecomprising a rod-like core of a high-resistance make-alive material anda closely fitting slotted sheath of insulating material, said sheathhaving a longitudinally extending slot extending through the Wallthereof and having a width such as to cause the meniscus of the cathodeto barely touch said core with a substantially zero pressure at somepoint below the level of the cathode.

4. A mercury-arc converter comprising a mercury cathode, an anodeseparated from said cathode, and a make-alive electrode projecting intosaid cathode, characterized by said make-alive electrode comprising arod-like core of a highresistance make-alive material and an enclosingslotted sheath of insulating material, said sheath having alongitudinally extending slot extending through the wall thereof andhaving a width such as to cause the meniscus of the cathode to barelytouch said core with a substantially zero pressure at some point belowthe level of the cathode.

JOSEPH SLEPIAN. HERBERT A. ROSE.

